1. Field of the Invention
The present invention relates to an intermediate transfer belt used for an image forming apparatus, e.g. a photocopier, facsimile, and printer, and to an image forming apparatus equipped with the intermediate transfer belt.
2. Description of the Related Art
Image forming apparatuses using an intermediate transfer belt as an intermediate transfer member are effective as color image forming apparatuses or multi-color image forming apparatuses, which outputs color prints by successively laminating and transferring a plurality of color images formed by color image information or multi-color image information. As for this type of the image forming apparatus, various image forming apparatuses using an intermediate transfer belt formed of a resin such as a polyimide resin or polyamide imide resin have been conventionally provided.
The intermediate transfer belt formed of the resin generally has high hardness. Therefore, the toner image (especially a center part of a character) receives concentration of stress to thereby prone to cause transfer failures called hollow defects of characters, for example, in a step for primary transferring a toner image from a photoconductor serving as an image bearing member to an intermediate transfer belt, and in a step for secondary transferring a toner image from an intermediate transfer belt to a recording medium.
As one of the methods for solving the problems of hollow defects of characters, giving elasticity to a surface of an intermediate transfer belt has been proposed. Specifically, by giving elasticity to a surface of an intermediate transfer belt, the surface of the intermediate transfer belt freely deforms corresponding to a thickness of a toner image so that the stress concentration to the toner image is reduced to thereby improve the problem of the transfer failure. Accordingly, the one in which an elastic layer formed of a flexible material such as a rubber is formed on a base has been used as an intermediate transfer belt for solving the problem of the transfer failure.
If the surface of the intermediate belt is the elastic layer, however, the lowest layer of the toner transferred from the photoconductor to the surface of the intermediate transfer belt adheres to the surface of the intermediate transfer belt due to the tackiness of the elastic layer, the adhered toner remains on the surface of the intermediate transfer belt without being transferred to a recording medium. Therefore, insufficient image density due to reduced transfer efficiency of the toner from the intermediate transfer belt to a recording medium, or image failures due to hollow defects of images occur.
To solve the aforementioned problem, Japanese Patent Application Laid-Open (JP-A) No. 07-234592 discloses an image forming apparatus equipped with an intermediate transfer belt that contains a base, an elastic layer formed on the base, and particles deposited on a surface of the elastic layer. By depositing particles on the surface of the elastic layer of the intermediate transfer belt, an exposed area of the surface of the elastic layer reduces to thereby reduces the tackiness of the elastic layer. Therefore, an amount of the toner remained on the intermediate transfer belt during transferring reduces, and the transfer efficiency improves.
Depending on the hardness of the intermediate transfer belt or the shapes of the particles deposited on the elastic layer, sufficient flexibility may not be attained, or the tackiness of the elastic layer may not be reduces. As a result, excellent transfer ability may not be attained. Especially, use of paper having irregularities on its surface has been currently increased not only use of common smooth paper. Therefore, the correspondence of the elastic layer to the irregularities on the paper becomes poor unless the elastic layer of the intermediate transfer belt elastic layer has sufficient flexibility. If the elastic layer has the poor correspondence, the density of the recess parts is lower than the density of the protruding parts in the image transferred from the intermediate transfer belt to the paper having irregularities on its surface, to thereby form uneven densities of the image corresponding to the irregularities of the surface.